921 research outputs found
On the classical-quantum correspondence for the scattering dwell time
Using results from the theory of dynamical systems, we derive a general
expression for the classical average scattering dwell time, tau_av. Remarkably,
tau_av depends only on a ratio of phase space volumes. We further show that,
for a wide class of systems, the average classical dwell time is not in
correspondence with the energy average of the quantum Wigner time delay.Comment: 5 pages, 1 figur
Comparación de fórmulas chilenas e internacionales para valorar el arbolado urbano
Ponce-Donoso, M (reprint author), Univ Talca, Fac Ciencias Forestales, Casilla 747, Talca, Chile.The appraisal of urban trees is a practice adopted in diverse cities of world. This survey compared international formulae: Council of Tree Landscape Appraiser (CTLA), Burnley, Helliwell and Standard Tree Evaluation Method (STEM) and three Chilean methods applied in municipalities of Concepcion, La Pintana, Maip (COPIMA), Nunoa and Penalolen, in 14 different trees located in Talca city (Chile). The objective was to identify the differences and similarities of the monetary result in the application of these formulae, which was realized by a professional. These were analyzed using a non parametric variance test of Kruskal - Wallis and the multiple comparisons Duncan test. It was possible to determine that the Chilean formulae did not present statistically significant differences with the international formulae of Burnley and CTLA; whereas Penalolen and COPIMA formulae did not present any difference when contrasted with Helliwell. In addition, the STEM formula presented differences with all the Chilean analyzed formulae. In the valuation by tree, statistically significant differences were obtained, which showed the independence of the used formula. The exception was when being applied to emblematic species or to species that stand-out in some amenity. Likewise, it was observed that the basic value continues having a high impact in the appraisal final result and the use of the statistical test applied allows extending this type of analyses
Statistical bounds on the dynamical production of entanglement
We present a random-matrix analysis of the entangling power of a unitary
operator as a function of the number of times it is iterated. We consider
unitaries belonging to the circular ensembles of random matrices (CUE or COE)
applied to random (real or complex) non-entangled states. We verify numerically
that the average entangling power is a monotonic decreasing function of time.
The same behavior is observed for the "operator entanglement" --an alternative
measure of the entangling strength of a unitary. On the analytical side we
calculate the CUE operator entanglement and asymptotic values for the
entangling power. We also provide a theoretical explanation of the time
dependence in the CUE cases.Comment: preprint format, 14 pages, 2 figure
How do wave packets spread? Time evolution on Ehrenfest time scales
We derive an extension of the standard time dependent WKB theory which can be
applied to propagate coherent states and other strongly localised states for
long times. It allows in particular to give a uniform description of the
transformation from a localised coherent state to a delocalised Lagrangian
state which takes place at the Ehrenfest time. The main new ingredient is a
metaplectic operator which is used to modify the initial state in a way that
standard time dependent WKB can then be applied for the propagation.
We give a detailed analysis of the phase space geometry underlying this
construction and use this to determine the range of validity of the new method.
Several examples are used to illustrate and test the scheme and two
applications are discussed: (i) For scattering of a wave packet on a barrier
near the critical energy we can derive uniform approximations for the
transition from reflection to transmission. (ii) A wave packet propagated along
a hyperbolic trajectory becomes a Lagrangian state associated with the unstable
manifold at the Ehrenfest time, this is illustrated with the kicked harmonic
oscillator.Comment: 30 pages, 3 figure
Resultados del tratamiento kinésico precoz y oportuno en un niño con Parálisis Facial
Paciente de 12 años, de sexo masculino, con diagnóstico médico de parálisis facial derecha, que ingresa al Servicio Universitario de Kinesiología de la Facultad de Medicina de la UNNE. Al inicio del tratamiento, el paciente presenta: alteración de la fascie con una marcada hipotonía de la hemicara afectada y una leve hipertonía en el lado contralateral. Se realizaron nueve sesiones de tratamiento kinésico basado en electroestimulación muscular selectiva indirecta con corriente exponencial y rectangular, asociada a ejercicios de reeducación muscular y masoterapia. Mediante esta técnica se logra mantener el trofismo muscular; una vez que el paciente recupera las funciones musculares, posteriormente desarrolla simetría y sincronía en la realización de los gestos de la mímica.El paciente logra su recuperación total en un corto considerado breve, sin ninguna complicación derivada de la utilización de electroestimulación
Majorization-based benchmark of the complexity of quantum processors
Here we investigate the use of the majorization-based indicator introduced in
[R. O. Vallejos, F. de Melo, and G. G. Carlo, Phys. Rev. A 104, 012602 (2021)]
as a way to benchmark the complexity within reach of quantum processors. By
considering specific architectures and native gate sets of currently available
technologies, we numerically simulate and characterize the operation of various
quantum processors. We characterize their complexity for different native gate
sets, qubit connectivity and increasing number of gates. We identify and assess
quantum complexity by comparing the performance of each device against
benchmark lines provided by randomized Clifford circuits and Haar-random pure
states. In this way, we are able to specify, for each specific processor, the
number of native quantum gates which are necessary, on average, for achieving
those levels of complexity. Lastly, we study the performance of the
majorization-based characterization in the presence of distinct types of noise.
We find that the majorization-based benchmark holds as long as the circuits'
output states have, on average, high purity (). In such cases, the
indicator showed no significant differences from the noiseless case.Comment: 12 pages, 15 figure
Measuring the Lyapunov exponent using quantum mechanics
We study the time evolution of two wave packets prepared at the same initial
state, but evolving under slightly different Hamiltonians. For chaotic systems,
we determine the circumstances that lead to an exponential decay with time of
the wave packet overlap function. We show that for sufficiently weak
perturbations, the exponential decay follows a Fermi golden rule, while by
making the difference between the two Hamiltonians larger, the characteristic
exponential decay time becomes the Lyapunov exponent of the classical system.
We illustrate our theoretical findings by investigating numerically the overlap
decay function of a two-dimensional dynamical system.Comment: 9 pages, 6 figure
Deep generative modeling for single-cell transcriptomics.
Single-cell transcriptome measurements can reveal unexplored biological diversity, but they suffer from technical noise and bias that must be modeled to account for the resulting uncertainty in downstream analyses. Here we introduce single-cell variational inference (scVI), a ready-to-use scalable framework for the probabilistic representation and analysis of gene expression in single cells ( https://github.com/YosefLab/scVI ). scVI uses stochastic optimization and deep neural networks to aggregate information across similar cells and genes and to approximate the distributions that underlie observed expression values, while accounting for batch effects and limited sensitivity. We used scVI for a range of fundamental analysis tasks including batch correction, visualization, clustering, and differential expression, and achieved high accuracy for each task
- …